Tricaine (MS-222, Tricaine-S), a water-soluble local anesthetic, is used commonly for sedation, immobilization, and anesthesia of poikilothermic animals and has been accepted as a common anesthetic for use in the cold-blooded animals. It has long been recognized as a valuable tool for the proper handling of these animals during manual spawning (fish stripping), weighing, measuring, marking, surgical operations, transport, photography, and research. Tricaine was developed by Merck as a sulfonated analog of benzocaine with high solubility in water. The main advantage of Tricaine is the short duration of action and rapid metabolism. There are many reports describing the use of Tricaine for anesthetizing poikilothermic animals because it is a safe agent for immersion anesthesia even though the other anesthetics such as ether, ethanol, thiopental, halothane, isoflurane, barbiturates also could be used. Amphibians could be anesthetized easily by immersion methods with Tricaine because the amphibian skin is extremely permeable and water is absorbed through the skin rather than ingested. Tricaine has been administered as an injectable agent also.